The method of radiation therapy using X-ray beams and ionizing particle beams has been known now for several decades. This method is used typically to treat malignant or other tumors or maladies within the body. Most recently the advent of stereotactic radiosurgery and stereotactic radiotherapy has been invoked with X-ray beams and charge particle beams to focally irradiate target volumes within the body based on three-dimensional calculation of the target volume from imaging and three-dimensional dosimetry using incoming beams from multiple directions towards the target volume. This is illustrated by the brochures from Radionics, Inc. on their stereotactic radiosurgery system.
Typical treatment planning systems, such as XKnife from Radionics, enable the phase space of possible X-ray beam angles to be manipulated on a computer workstation and visualized graphically. In addition, the selection of collimator sizes and target isocenter, which is a convergent point for incoming beams, can be adjusted. Once a multiple set of beams has been set up to a specified and calculated target volume, the dosimetry of radiation associated with these beams can be thereafter calculated and the dose at each point within the volume, including points in the tumor target volume as well as points in neighboring normal tissue, can be determined. Typically, such plans seek to get the maximum radiation and maximum surface dose homogeneity on a target volume, while at the same time minimizing the dose to critical volumes and structures in the vicinity of the aberrant target volume. Radiation-sensitive structures such as the brain stem, optic globes, and nerves are particularly important to take into account in such plans. Reduction of the geometric intersection of the beams from acceptable input directions to these critical structures is part of the plan. Typically, these plans are done by physicists and radiation therapists who have skill in being able to select the appropriate beam phase space of incoming angles, and thereby set up the plan as quickly as possible. Very involved plans where critical structures surround the tumor volume are much more difficult and can require significant amount of human labor, even with a high-powered computer graphic workstation.
Thus, it is desirable to be able to automate the selection of phase space of incoming beam directions to produce in an automatic fashion a dosimetry plan and plan of incoming directions to both maximize the effective dose on a target volume and minimize the effect of radiation on critical or normal structures in the vicinity of the target volume. It is one of the objectives of this patent application to describe a method whereby such an automatic planning system can be set down. The use of geometric constraints during a computation of the treatment plan is invoked, and the use of threshold dosimetric criteria involving the coverage of the target volume and the involvement of critical surrounding structures is used to search in the phase space and optimize the plan automatically.
It is the objective of this patent application also to describe a computational methodology that can be exercised on a computer workstation whereby such an automatic dosimetry plan can be utilized.